Update JMXFetch to 0.30.1

dd-java-agent/agent-jmxfetch/agent-jmxfetch.gradle

@@ -4,7 +4,7 @@ plugins {
 apply from: "${rootDir}/gradle/java.gradle"
 
 dependencies {
-  compile('com.datadoghq:jmxfetch:0.30.0'){
+  compile('com.datadoghq:jmxfetch:0.30.1'){
     exclude group: 'org.slf4j', module: 'slf4j-log4j12'
     exclude group: 'log4j', module: 'log4j'
   }

gradle/dependencies.gradle

@@ -7,6 +7,8 @@ ext {
 
     slf4j      : "1.7.25",
     guava      : "20.0", // Last version to support Java 7
+
+    // When upgrading for security fixes, ensure corresponding change is reflected in jmxfetch.
     jackson    : "2.9.9.3", // https://nvd.nist.gov/vuln/detail/CVE-2019-14379
 
     spock      : "1.3-groovy-$spockGroovyVer",